1. Field of the Invention
The present invention relates to an apparatus for stimulating the vestibular system, and, in particular, to a non-invasive stimulation electrode assembly having a portion that fits within the ear canal to stimulate the vestibular system and to a system using such an electrode assembly.
2. Description of the Related Art
The vestibular system is responsible for the detection of the position and motion of the head in space. The semicircular canals, which are located in the inner ear, are the sensory organs of the vestibular system, and collect head position and motion information and transmit it to the central nervous system via the eighth cranial nerve. Disorders of the vestibular system may result in physiological disorders such as dizziness, vertigo, and nausea, with symptoms ranging in severity from mild to completely debilitating.
Stimulation of either the semicircular canals, the utricle, saccule, or other otolith organs, as well as stimulation of the nerve fibers leading from these organs or the eighth cranial nerve, or combinations thereof result in a sensation of movement in normal subjects. Moderate stimulation of the vestibular system may cause perceptions of mild movement that are not unpleasant, but can have beneficial properties, such as promoting a sleep state in a patient.
Many techniques for stimulating the vestibular system exist. These methods include calorimetric, chemical, and electrical approaches. Calorimetric and chemical stimulation typically take the form of direct application of a warm solution or a chemical compound, either directly or indirectly, to the eighth cranial nerve. Electrical stimulation of the vestibular system typically includes the placement of an electrode on the surface of the skin, e.g., over the mastoid bone behind the ear, or the piercing of the tympanic membrane with an electrode for direct stimulation of the semicircular canals. It is also known to stimulate the vestibular system by invasive electrodes implanted within the inner ear.
Stimulation of the vestibular system via a surface electrode often causes non-specific activation of nerves and muscles that result in unpleasant experiences for the patient. For example, surface electrode stimulation of the vestibular system may result in non-specific activation of facial muscles and/or the auditory aspect of the eighth cranial nerve, causing involuntary twitches and auditory perceptions, respectively. While direct electrode stimulation of the semi-circular canals is specific, the placement of an electrode through the tympanic membrane and/or within the inner ear can be quite unpleasant for the patient, and also presents an opportunity for infection of or physical damage to the inner ear, tympanic membrane, or other components of the ear.
Thus, a long standing need exists within the medical field for a system that allows for the specific and non-invasive activation of the vestibular system that is comfortable enough for a patient to wear for an extended period time, such as during sleep, and during periods of quiet resting. In addition, such a system should allow for the delivery of a wide variety of stimulation frequencies and waveforms to the vestibular system of the inner ear. The system should also be comfortable for the patient even when the system is disposed between the patient and an underlying support, for example when the patient's head is lying on a pillow with the stimulation system situated between the head and pillow. In addition, the system should remain firmly in place so that the stimulating energy is delivered to the desired anatomical location despite normal movement and contact forces, such as tossing and turning during sleep and when attempting to fall asleep.